This invention relates to improvements in fabrication processes for making magnetographic recording heads.
The commercial production of recording heads for high resolution magnetography (i.e., &gt;100 lines per inch) for commercial applications such as printing, requires fabrication techniques and processes that can provide consistantly and economically reliable yields.
More specifically, a recording head structure such as that described in U.S. Pat. No. 4,025,927 to Nelson requires the formation of very fine recording elements arranged in an array with spacings as small as 3-4.times.10.sup.-3 inch. As described therein, the recording of minute magnetic zones or pixels on a magnetic recording medium is accomplished through the geometric "thinning down" of each of the recording elements at their respective recording zones. Hence, the "center" of the recording current is directed toward and thus closer to the magnetic medium at the recording zone, resulting in a more intimate interaction between the magnetic field of the recording current and the magnetic medium.
In such a recording head structure the many individual closely spaced apart recording elements have dimensions on the order of 1.5-4.times.10.sup.-3 in. wide and 0.1-0.5.times.10.sup.-3 in. thick (at the recording zone), and yet are 0.5-3 inches long.
It is appropriate to employ the so-called bi-metal etch foil technology to fabricate such recording heads. In such a technique, each side of a sheet of copper foil may be coated with a photoresist material and optically exposed to a designed pattern corresponding at least in part to the intended arrangement of conductive recording elements. Subsequently, the exposed photoresist is removed (for a positive photoresist or vice versa for a negative photoresist) and the foil then subjected to a nickel plating process step that results in the deposition of say 0.1-0.5.times.10.sup.-3 in. thick nickel on the bared copper surfaces of at least one of the sides of the foil. At this point both sides of the copper foil are entirely coated with either photoresist or nickel, neither of which is affected by the etching solutions utilized to dissolve away the copper.
Essentially, the front and rear patterns are designed such that each recording element is sandwiched in between nickel and/or photoresist coatings. As the elements extend away from the recording zone, there size can increase and the elements can thus be arranged to fan-out. At the recording zone the coating of say the back side (i.e., nickel or any other back-side suitable coating/filling material used, such as photoresist material) only is discontinued for a predetermined length i.e., on the order of 3-8.times.10.sup.-3 inches. Removal of the underlying copper at the recording zone creates an indentation in each of the recording elements constituting the thinning of the recording element down to the 0.1-0.5.times.10.sup.-3 inch thick nickel layer on the front side. Thus, this removal of the copper at the recording zone effectively divides the copper foil into two parts. The two portions are, therefore, held together essentially only by the very thin and delicate unsupported nickel elements. This construction, i.e., the relatively immense areas of copper foil on either side of the very thin nickel bridges holding these masses of copper together, is extremely fragile and as a result impractical with regard to customary process steps and handling procedures.
Therefore, what is needed is an improved fabrication process that would permit reliable and relatively inexpensive production of such recording heads at substantially higher production yields.